Field of Invention
The present disclosure relates to an electrode-voltage waveform controlling method. More particularly, the present disclosure relates to the cooperative-electrode driving technique of digital microfluidic systems.
Description of Related Art
In recent years, introduction of electronic automation in digital microfluidics (DMF) systems has intensified them as a prospective platform for managing the intricacy of large-scale micro-reactors that have underpinned a wide variety of chemical/biological applications such as immunoassays, DNA sample processing and cell-based assays. Yet, to further position DMF in high throughput applications like cell sorting and drug screening, the velocity (νdroplet) of droplet transportation must be improved, without compromising its strong reliability and controllability features. The limitation of a droplet transportation velocity depends on the actuation voltage and the size of a droplet. Empirically it barely reached 2.5 mm/s at an actuation voltage below 20 V.
Under the principle of electrowetting-on-dielectric (EWOD), νdroplet is determined by the following parameters: (1) surface roughness and hydrophobicity of the fabricated chip; (2) hydro-dynamics of droplets that can be chemical reagents or biological species with very different compositions; (3) strength of the electric field for surface-tension modulation, and (4) viscous mediums causing drag forces that increase the power required to manipulate the droplets.
A few attempts have been made to address the problems based on hardware. One hardware solution is using the co-planar electrodes as a top-plate-less DMF system to reduce the viscous drag forces between the liquid-solid interfaces. Another hardware solution is using a water-oil core-shell structure to achieve high νdroplet. The aforementioned hardware solutions are vulnerable to contamination and evaporation that are intolerable for essential applications like polymerase chain reaction (PCR). Another hardware solution is tailoring the electrode shape to boost νdroplet.
Instead of hardware modification, unguided DC-pulse train could already regulate νdroplet for non-deformed droplet manipulation by adjusting the actuation signal. However, νdroplet was lower than that of DC. Another work designated residual charging was capable to execute multi-droplet manipulation, but the waveform parameters were not studied for an optimum νdroplet.
Naturally, elevating the electrode-driving voltage can raise the electric field to accelerate νdroplet, but still, compromising the chip lifetime due to dielectric breakdown, and the cost of the electronics which goes up with their voltage affordability. To our knowledge, there is no electrode-driving technique that can concurrently enhance νdroplet and elongate electrode lifetime of a EWOD device.